(* Title: HOL/Auth/Event
ID: $Id$
Author: Lawrence C Paulson, Cambridge University Computer Laboratory
Copyright 1996 University of Cambridge
Theory of events for security protocols
Datatype of events; function "spies"; freshness
"bad" agents have been broken by the Spy; their private keys and internal
stores are visible to him
*)
theory Event = Message
files ("Event_lemmas.ML"):
consts (*Initial states of agents -- parameter of the construction*)
initState :: "agent => msg set"
datatype
event = Says agent agent msg
| Gets agent msg
| Notes agent msg
consts
bad :: "agent set" (*compromised agents*)
knows :: "agent => event list => msg set"
(*"spies" is retained for compatibility's sake*)
syntax
spies :: "event list => msg set"
translations
"spies" => "knows Spy"
axioms
(*Spy has access to his own key for spoof messages, but Server is secure*)
Spy_in_bad [iff] : "Spy \<in> bad"
Server_not_bad [iff] : "Server \<notin> bad"
primrec
knows_Nil: "knows A [] = initState A"
knows_Cons:
"knows A (ev # evs) =
(if A = Spy then
(case ev of
Says A' B X => insert X (knows Spy evs)
| Gets A' X => knows Spy evs
| Notes A' X =>
if A' \<in> bad then insert X (knows Spy evs) else knows Spy evs)
else
(case ev of
Says A' B X =>
if A'=A then insert X (knows A evs) else knows A evs
| Gets A' X =>
if A'=A then insert X (knows A evs) else knows A evs
| Notes A' X =>
if A'=A then insert X (knows A evs) else knows A evs))"
(*
Case A=Spy on the Gets event
enforces the fact that if a message is received then it must have been sent,
therefore the oops case must use Notes
*)
consts
(*Set of items that might be visible to somebody:
complement of the set of fresh items*)
used :: "event list => msg set"
primrec
used_Nil: "used [] = (UN B. parts (initState B))"
used_Cons: "used (ev # evs) =
(case ev of
Says A B X => parts {X} Un (used evs)
| Gets A X => used evs
| Notes A X => parts {X} Un (used evs))"
use "Event_lemmas.ML"
method_setup analz_mono_contra = {*
Method.no_args
(Method.METHOD (fn facts => REPEAT_FIRST analz_mono_contra_tac)) *}
"for proving theorems of the form X \<notin> analz (knows Spy evs) --> P"
end